Many schemes exist to allocate resources in the field of bus systems; i.e. to assign channels to devices wishing access to the bus. Some schemes relate to allocating a complete bus for the duration of a connection. This can be referred to as time-sharing a bus as opposed to a TDM bus. U.S. Pat. No. 3,710,351 dated Jan. 9, 1973 to N. Nakamura discloses one system for allocating a bus on a time-shared basis. That patent teaches the use of two buses (one for addressing and one for data) and teaches the use of a priority system whereby addresses are compared to determine the priority of access to the data bus. Such a system is described in more detail in aforementioned U.S. Pat. No. 3,710,351 to which attention is directed.
In another scheme, a line (bus) disengagement detecting circuit is used to detect whether or not the line is idle. If the line is idle and a unit wishes to transmit on the line, it transmits a line-use request signal and a signal indicative of the address peculiar to the unit every bit from the highest or lowest place at fixed time intervals. A superposition detector is used to determine whether or not a signal transmitted by the unit has been superimposed on another signal on the bus and priority can be determined by comparing addresses of any competing units. Such a system is described in more detail in U.S. Pat. No. 3,796,992 dated Mar. 12, 1974 by H. Nakamura et al to which attention is directed.
Another scheme is to use a common controller. Each device is arranged to communicate with the common controller on an interrupt basis by issuing requests for access thereto on a common interface or communications channel therewith. Each device has an assigned interrupt number and includes means, effective when issuing a request for access, for comparing such number with other interrupt numbers presented to the interface in connection with conflicting requests for access by other devices in the system. Each device also includes means for proceeding with, or abandoning such request according to the result of such comparison. Such a scheme is described in more detail in U.S. Pat. No. 3,818,447 dated June 18, 1974 by D. J. Craft, to which attention is directed.
Another scheme is known by the tradename "Ethernet". This scheme is somewhat similar to the aforementioned U.S. Pat. No. 3,796,992 except that there is no priority determination. In the Ethernet system, when a station wishes to transmit, the presence of other transmissions on the data bus is detected and transmission is delayed until no other transmissions are detected. Once a transmission is initiated if interference or collision is detected with a transmission initiated at about the sam time by another station, transmission at each station is stopped. A random number generator is employed at each station to determine an interval of time at the completion of which the next attempted transmission will occur so as to resolve the contention for the bus. Such a scheme is described in more detail in U.S. Pat. No. 4,063,220 dated Dec. 13, 1977 by R. M. Metcalfe et al to which attention is directed.
One scheme for seizing an idle time slot in a TDM loop, or ring, communication system is described in U.S. Pat. No. 4,383,315 dated May 10, 1983 by H. C. Torng. Such a scheme uses a master node and other nodes along with statistically determined time delays. Such a scheme is described in more detail in the aforementioned patent to which attention is directed.
U.S. Pat. No. 4,458,314 dated July 3, 1984 by G. J. Grimes discloses a bus sharing scheme for a packet bus employing a separate arbitration bus and a central controller. Each unit (port) has a unique priority code which it synchronously and sequentially applies to the arbitration bus beginning with the most significant digit. After the application of all digits, only the requesting port having the highest code remains in contention and seizes the data bus.
Other patents relating to this general topic and to which attention is directed are as follows: U.S. Pat. No. 4,463,351 dated July 31, 1984 by V. Chiarottino; and U.S. Pat. No. 4,564,838 dated Jan. 14, 1986 by G. F. Boulogne et al.